First-principles study on the effect of atomic swap on the electronic properties and quantum capacitance of Sc2CF2 monolayer

Two-dimensional materials have attracted great attention due to their excellent properties. In this paper, we conducted a theoretical study on the atomic swap within Sc2CF2 MXene. The geometric structure, electronic properties and quantum capacitance of Sc2CF2-SC↔F, Sc2CF2-SC↔Sc, and Sc2CF2-SF↔Sc monolayers are investigated by first-principles calculation. Sc2CF2-SC↔Sc and Sc2CF2-SF↔Sc monolayers form Frenkel-type defect structure after optimization. Pristine Sc2CF2 is an indirect semiconductor, while the atomic swap has no effect on the semiconductor character of Sc2CF2-SC↔F, Sc2CF2-SC↔Sc, and Sc2CF2-SF↔Sc monolayers. Especially, the atomic swap between C and Sc atoms make Sc2CF2-SC↔Sc monolayer become a narrow direct semiconductor. The quantum capacitances in aqueous and ionic/organic systems are further investigated. In aqueous and ionic/organic electrolyte, Sc2CF2 and Sc2CF2-SF↔Sc are more suitable for cathode materials, while Sc2CF2-SC↔Sc monolayer is suitable for anode materials. Sc2CF2-SC↔F is transformed from a potential cathode material to a potential electrode material for symmetric supercapacitors with the extension of voltage. The effective mass and work function of the systems are further explored. The electronic properties and quantum capacitance of Sc2CT2 with mixed termination groups are also investigated.